The present invention relates to a functionally improved battery and, more particularly, to a battery which includes a flexible thin layer open liquid state electrochemical cell and an electronic chip device integrally formed on or within the battery, which chip improves a functionality of the battery. The present invention further relates to a method of making a functionally improved battery. Specifically, the functional improvements of the batteries of the present invention increase the useful life (service) of the battery and make the battery a more reliable power source. By reliability, as used herein, is meant that a power output from the battery is less prone to undesired changes over time than a prior art battery.
The ever-growing development of miniaturized and portable electrically powered devices of compact design such as, for example, cellular telephones, voice recording and playing devices, watches, motion and still cameras, liquid crystal displays, electronic calculators, IC cards, temperature sensors, hearing aids, pressure sensitive buzzers, etc., generates an ever-growing need of compact thin layer batteries for their operation. Therefore, there is a need for reliable thin layer electrochemical cells to be used as batteries. Reliability is especially critical in, for example, sensitive medical equipment and communication devices.
Batteries can be broadly classified into two categories in which the batteries of the first category include wet electrolytes (i.e., liquid state batteries), whereas batteries of the second category include a solid state electrolyte. Although solid state batteries have an inherent advantage, they do not dry out and do not leak, they suffer major disadvantages when compared with liquid state batteries since, due to limited diffusion rates of ions through a solid, their operation is temperature dependent to a much larger extent, and many operate well only under elevated temperatures; and, the limited diffusion rates thus described, characterize solid state batteries with low ratio of electrical energy generated vs. their potential chemical energy.
Liquid state thin layer batteries typically include a positive and negative active insoluble material layer put together with a separator interposed therebetween, which separator is soaked with a liquid electrolyte solution, thus functioning as an electrolytic liquid layer. Such batteries, an example of which is disclosed in U.S. Pat. No. 4,623,598 to Waki et al., and in Japanese Pat. No. JP 61-55866 to Fuminobu et al., have to be sealed within a sheathing film to prevent liquid evaporation, and are therefore closed electrochemical cells. Being closed cells, these batteries tend to swell upon storage due to evolution of gases which is a fatal problem in thin layer batteries having no mechanical support, the pressure imposed by the accumulated gases leads to layer separation, thus turning the battery inoperative. Means to overcome this problem include (i) the use of a polymer increased viscosity agent, such as hydroxyethylcellulose, applied to adhere (i.e., glue) the battery layers together, thus to overcome the inherent problem of such batteries imposed by lack of solid support; and, (ii) addition of mercury to prevent the formation of gases, especially hydrogen. However, the polymer is limited in its effectiveness and the mercury is environmentally hazardous.
A way to solve the above described limitation was disclosed in U.S. Pat. No. 3,901,732 to Kis et al. in which a gas-permeable electrolyte-impermeable polymeric material which allows venting of undesirable gases formed within the battery while preventing any electrolyte loss from the battery is used as a sheathing film to enclose the battery cell.
However, a more direct and efficient way to avoid undesired gas accumulation in liquid state thin layer batteries is to provide these batteries as open cells for facilitated release of gases, while at the same time to
The structure, manufacture and integration into electronic applications of such a flexible thin layer open liquid state electrochemical cell are described in detail in U.S. Pat. Nos. 5,652,043; 5,811,204 and 5,897,522, all to Nitzan, which are incorporated by reference as if fully set forth herein.
A disadvantage shared by all battery types is that use of the battery after the voltage of the cell(s) drops below the minimum required level for the device operated thereby is infeasible. Generally, a potential difference between the poles of the battery still exists at this point. It is therefore desirable to attach an external chip device to the battery to allow utilization of this power.
The attachment of chips to printed circuit boards (PCB) may be effected by welding or by what is known as a flip-chip technology.
Welding requires heating of metal contacts on both the PCB and the chip device to fuse them to a connecting conductive wire, typically a gold wire or an aluminum wire. The process is technically complex, requires the use of welding ultrasound welding devices, and the input materials are expensive. As a result, the welding option is commercially unattractive with respect to battery manufacture.
Flip chips, for example of the type disclosed in U.S. Pat. No. 5,059,553 which is fully incorporated herein by reference, rely upon the use of conductive protrusions or bumps which can fuse to a chip device when heat or pressure are applied. This technology is easier to implement than welding and is commercially more desirable. Recent advances in flipchip technology include, but are not limited to, the use of polymer flip-chips as described in F. Kuleza and R. Estes (1997) “A Better Bump: Polymer's Promise to Flip Chip Assembly” Advanced Packaging, HIS Publishing which is fully incorporated herein by reference.
Neither welding nor flip-chip technology were so far employed with batteries so as to form a battery having an integral chip thereon.
There is thus a widely recognized need for, and it would be highly advantageous to have, a functionally improved battery having an integrated chip so as to improve its functionality.